1. Field of the Invention
The present invention relates generally to natural gas pipe lines or the like, having a flow control valve therein for controlling flow. More particularly, it relates to a unique device that is responsive to a drop in pipe line pressure, such as might occur upon a rupture in the pipe line, to automatically close an upstream flow control valve, utilizing the upstream pressure from the pipe line to do so.
2. Description of the Prior Art
It is customary to partition natural gas pipe lines at regular distances by means of flow control valves, which may be of the ball valve or other selected type, so that when a burst in the pipe line occurs the escape of the natural gas can be stopped by means of a not too distant sealing device. A burst is manifested by a drop in pressure toward the site of the burst, which drop is sensed by suitable control devices and is utilized for the control of the flow control valve that is positioned upstream relative to the side of the burst.
For the purpose of measuring relatively small pressure differences at rather high absolute pressure, the Barton cells are known, and such operate with two measuring bellows exposed to the pressures to be compared. However, Barton cells normally cannot be considered for the present purpose because the control devices must be arranged in open ground along the natural gas pipe line, and diaphragm or bellows switch elements are less suitable than is desirable for the low temperatures often encountered. Moreover, the pressure in a natural gas pipe line is usually rather high for the utilization of such switch elements, so that an interposed pressure-reducing valve would normally be required. This will increase the total cost, and adds to the susceptibility of the device to defects and operating failures.
A control device is also known which operates in the manner of a scanning device, and which compares at regular distances the pressures at two points of the natural gas pipe line. When a difference occurs, a switch for actuating the flow control valve is actuated.
The actuation of the flow control valve requires some outside energy, e.g., electric energy, for producing the hydraulic pressure for a hydraulic actuator or for the direct electrical actuation of the flow control valve. Such devices are sensitive to failures of the energy supply system, and thus could in the case of a pipe burst then at best be operated by hand, which would necessitate the presence of an operator at the flow control valve adjacent to the site of the burst.